Permanent magnet electrodynamic loud-speaker



Oct. 0,

E. L. RUHSSELL 2,524,836

. PERMANENT MAGNET ELECTRODYNAMIC LOUD-SPEAKER Filed April 2, 1947 2Sheets-Sheet 1 uvvmroa Enm. L. RUSSELL Arman 21 Oct.v 10,1950 E. L.RUSSELL 2,

' PERMANENT MAGNET ELECTRODYNAMIC LOUD-SPEAKER Filed April 2,1947 2Sheets-Sheet 2 INVENTOR. EARL L. RvssELL r v BY i 1" I 601mm, 9* 77761407,

i z Fh'ToRNEY-s Patented Oct. 10, 1950 PERMANENT MAGNET ELECTRODYNAIWICLOUD SPEAKER Earl L. Russell, Cleveland, Ohio, assignor to The RolaCompany, Ina, Cleveland, Ohio, at corporation of Ohio Application April2, 1947, Serial No. 738,894

This invention relates to loud speakers, and particularly to loudspeakers of the permanent magnet type.

Loud speakers utilizing a permanent magnet for the field structure aresubject to the accumulation of foreign particles in the confined spacebetween the voice coil forms and the opening therefor in the front plateof the magnetic structure. Great care must be exercised in themanufacture of the loud speaker to avoid the possibility of magneticparticles being attracted to and held by the magnetic structure, asotherwise their presence would interfere with the normal reciprocatingmovement of the voice coil within the air gap and cause a scratchingnoise in the reproduction. The centering of the voice coil form withinthe air gap is also important. The con struction utilized, however, mustbe sufficient not only to maintain the proper spacing between thecomponent parts, but must enable the speaker to withstand rough handlingincident to the packing and shipment of the loud speakers from themanufacturer to the set manufacturer, and then to the ultimate user.

An effort heretofore has been made to overcome the aforementioneddifficulty by permanently fastening the cone and housing assembly tothefield assembly after the voice coil form has been centered by meansof a gauge with respect to the Claims. (Cl. 179-4155) an end view of thefield structure as viewed in the direction indicated by the arrows 3-3in Fig. 2; Fig. i is a rear view of the assembled loud speaker with aportion thereof broken away; Fig. 5 is a section taken on a planeindicated by the line 5-5 in Fig. i, and Fig. 6 is a section taken on aplane indicated by the line 6- 6 in Fig. 4.

The loud speaker with which the present invention is shown has apermanent magnetic field which includes a shell type core, indicated ingeneral at H], and preferably comprises a strip of metal that is bent toform an open frame having a front plate H, a back plate It, a top plate[3 and a bottom plate It. The front plate has an opening l5 therein andthe back plate has a pole piece [6 extending into the shell andsubstantially parallel to the top and bottom plates thereof. The polepiece terminates in a pole tip H which is concentrically disposed withinthe opening l5 and cooperates therewith to provide the air gap in whichthe voice coil is adapted to operate in the usual way. The pole piece Itis held within central position within the shell by means of a resilientcup-shaped member that is so1-,

dered or otherwise securely fixed to the back of the front plate and isadapted to engage a tapered surface 2i on the pole piece to exerttension thereagain'st, so as to hold it firmly in central .p-ositionwith respect to the shell.

' is attached. The form carries the usual voice in order to get at thespace in the region of the 7 air gap for the purpose of freeing the gapof foreign particles or in order to re-center the voice coil. In loudspeakers utilizing a permanent magnet, such occurrence is apt to besufficiently frequent to consitute a major item in the servicing andrepairing of loud speakers.

An object of the present invention is to provide a loud speaker whereinthe cone or diaphragm and its associated housing assembly can be removedfrom the field assembly without destroying or disturbing therelationship of the parts forming the diaphragm assembly, therebyenabling the field structure, in the region of the air gap, to beeffectively cleaned or centered and the parts re assembled in anexpeditious manner.

Referring now to the drawings, Fig. l is-a side elevation of a loudspeaker embodying the present invention; Fig. Z'is an exploded view inside'elevation of the assembly shown in Fig. 1; Fig. 3 is threadedengagement with registering openings in the base of the cone housing. Asis shown in Fig. 2, the openings 3% are larger than the diameter of thethreaded shank of the fastener 35, as a result of which adjustment maybe made between ,the field structure and the cone assembly whenever thescrews are loosened.

The foregoing describes the component parts of the loud speaker, theassembly ofwhich may be made in accordance with that disclosed anddescribed in my copending application Serial No. 127,961, filed November17, 1949,- and assigned to The Rola Company, Inc. Briefly in carryingout the method of assembly, the plate 31 is staked or otherwise securelyfastened to the front plate H, as by bosses 4!] which are extruded fromthe front plate and are adapted to enter correspondingly shaped openingsin the plate 31'. Additionally, the attachment is made by threadedfastening members 4!, as is shown in Fig. 3. The plate and shell as aunit are then fastened to the cone housing 32 by means of thesecuringmembers 35, these being accessible from the rear of the housingas is shown in Fig. 4, inasmuch as the plate 31 is wider than thematerial of which the shell IE] is made.

After the shell has been assembled to the housing, then the pole piecei6 is centrally located therein by means of a suitable gauge placedbetween the pole tip and the wall of the Opening l5, and is locked inplace by the resilient center ing member 29, after which solder isapplied to hold the pole piece to the back wall of the shell and to holdthe centering member to the front plate of the shell.

After the assembly of the magnetic structure, the centering member iscemented at its outer periphery to the base 3| of the cone housing,while being centered with respect to the axis of the pole tip by meansof a gauge that is inserted within the air gap. The assembly of the coneand its associated voice coil form to the centering member 30 is made byapplying cement to the neck of the cone on the outer portion thereof andthen inserting the voice coil form into the air gap, using a customarycentering gauge to space it with respect to the pole piece. The form isinserted until the centering member fits snugly against the neck of acone, whereupon the cement operates effectively to join the two partstogether. While the centering gauge is still in position, the base ofthe cone is cemented to the cone housing and sealed by means of thegasket 33 which is cemented thereto.

In the event of the voice coil form being inaccurately centered withrespect to the pole piece, then it is only necessary to loosen thescrews 35 and move the field assembly with respect to the cone assembly,using the customary centering gauge between the voice coil form and thepole tip, and then tightening the members 35.

In the event of metallic particles or other foreign particles beingentrapped between the pole tip and the voice coil form, then uponremoval of the fastening members 35, the field structure may be removedas a unit from the cone assembly, the air gap may be thoroughly cleanedand the parts reassembled by means of a centering gauge and replacementof the screws 35.

Heretofore it has been necessary to destroy the,

cone, together with its associated centering member, voice coil andvoice coil form in order to relocate a form with respect to the walls ofthe air gap, or to make the air gap accessible for cleaning purposes. Anadvantage of the present invention, however, is that the adjustment andcleaning can be made without destroying any of the component parts, andwithout disturbing the connection between the cone, the centering memberand the housing. Thus, a saving is made in parts and considerablereduction is effected in the time required to rebuild the loud speaker.Moreover, the invention is advantageous in that the cone assembly andfield structure may be quickly adjusted merely by the insertion Of acentering gauge between the voice coil form and the pole tip at the timeof tightening of the fastening members, which are readilyaccessible'from the exterior part of the unit.

I claim:

1. A loud speaker having a diaphragm, a voice coil form attachedthereto, a centering member extending from the form radially thereof, ahousing for the diaphragm, means for attaching the outer portion of thediaphragm to the housing, a field structure embodying a permanent magnetand including a shell-type core having an open ing for receiving thevoice coil form, a pole piece disposed within said shell type core, acentering member secured within said shell type core and adapted tofixedly enclose the tip of said pole piece, thereby securing it firmlyin central position with respect to said shell, a plate rigidly attachedto the core and removable loose fitting fastening means for connectingthe plate to the a housing.

2.. A loud speaker having a diaphragm, a voice coil form attachedthereto, a centering member extending from the form radially thereon, ahousing for the diaphragm, means for attaching the outer portion of thediaphragm to the housing, a field structure including a permanentmagnetic type core having an opening for receiving a voice coil form,said core embodying an open frame of uniform width, a pole piecedisposed within said core frame, a resilient centering member securedwithin said core frame and adapted to fixedly enclose the tip 0f saidpole piece thereby retaining it firmly in central position with respectto said core frame, a plate rigidly attached to the frame and beingwider than the frame, and loose fitting fastening means for detachablyconnecting the plate to the housing, said means being accessible fromthe exterior of said field structure.

3. A loud speaker having a permanent magnetic field structure includinga core having a front plate with an opening therein, and a back; plate,a pole piece extending from the back plate and having a pole tipdisposed within said open ing and disposed concentrically with respectthereto, a centering member secured to the front plate within said corestructure and adapted to fixedly enclose said pole tip thereby retainingit firmly in central position with respect to said core structure, adiaphragm having a voice coil and a centering member attached thereto,the form being positioned between the pole tip and the wall of saidopening, a housing, means for rigidly connecting the centering memberand the diaphragm to the housing, a member rigidly fastened to the frontplate and disposed between it and the housing and having an opening inregistration with that in the front plate through which the voice coilform extends, said member having spaced openings therein, and saidhousing having openings in registration with the lastnamed openings,threaded fastening members extending through said last-mentionedregistering openings for securing the magnetic field structure to thehousing, the openings in the member being larger than thecross-sectional area of the associated fastening members, whereby themember and field structure as a unit may be adjusted radially withrespect to the voice coil form.

4. A loud speaker having one unit comprising a permanent magnetic fieldstructure, including a core, a pole piece, a resilient centering membersecured within said field structure and adapted to fixedly enclose thetip of said pole piece thereby firmly retaining it in central positionwith respect to said field structure, and a plate connected together asa unit, and another unit comprising a diaphragm, a voice coil form, acenter- 5. A loud speaker having a conical diaphragm,

a Voice coil form attached thereto, a flaring housing about thediaphragm, meansfor attaching the outer portion of the diaphragm to theouter portion of the housing, a centering member for the voice coil formextending radially outward therefrom and attached to the inner portionof the housing, a field structure of the shell type having a front withan opening for receiving the voice coil form, a pole piece disposedwithin said field structure, a resilient centering member secured withinsaid field structure and adapted to fixedly enclose the tip of said polepiece thereby firmly retaining it in central position with respect tosaid field structure, a plate resting against said front and rigidlyattached thereto and overhanging opposite sides of the field structure,and

'6 loose fitting fastening means at the overhanging portions of saidplate for detachably connecting the plate to the inner portion of thehousing, said means being accessible from the exterior of said fieldstructure.

' EARL L. RUSSELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,721,023 Jensen July 16, 19291,859,518 Kingsford May 24, 1932 1,864,809 Dempster et a1. June 28, 19321,872,261 Engholm Aug. 16, 1932 1,881,324 Metoalf Oct. 4, 1932 1,886,816Jensen Nov. 8, 1932 1,891,404 Engholm Dec. 20, 1932 1,897,294 Bernard -1Feb. 14, 1933 1,905,702 Hardisty Apr. 25, 1933 1,906,196 Fisher Apr. 25,1933 1,941,477 Jensen Jan. 2, 1934 1,948,361 Sollie Feb. 20, 19342,027,473 Creager Jan. 14, 1936 2,174,355 Sundstrom Sept. 26, 19392,200,490 Cornwell May 14, 1940

